Final answer:
The TP53 gene, encoding the p53 protein, is the most frequently encountered oncogene in human tumors, with mutations found in more than half of human cancers. It plays significant roles in DNA repair, cell cycle regulation, and apoptosis. A mutated TP53 gene leads to unregulated cell growth and a high risk of cancer.
Step-by-step explanation:
The most frequently encountered oncogene in human tumors is the gene encoding the p53 protein, which is also known as TP53 in humans. Mutations in TP53 are associated with a wide array of human cancers such as pancreatic, lung, renal cell, and breast cancer. It is estimated that more than half of human cancers involve a mutated p53 gene, making it a very common genetic alteration in cancer.
The p53 protein is critical for cellular functions such as DNA repair, cell cycle regulation, and apoptosis. When the gene is mutated, these processes can fail, leading to unregulated cell proliferation and potentially cancer. Li-Fraumeni syndrome (LFS) patients, who typically carry at least one mutated p53 allele, have a nearly 100% lifetime risk of developing cancer, often starting in childhood. In laboratory cultures, cells with mutated p53 genes exhibit characteristics of cancer cells, including uncontrolled cell growth and reduced apoptosis.
TP53 contrasts with other oncogenes such as HER2, which also plays a role in the development of cancer. For instance, HER2 overexpression is seen in approximately 20 percent of human breast cancers due to gene duplication. Treatments like the drug Herceptin (trastuzumab), which targets HER2, have been developed to manage cancer growth by harnessing the immune system to remove HER2 and thereby control cell signaling.